There are a number of potential technical problems with the results of the official breath test conducted at the station or Adult Detention Center, which is different than the PBT offered on the side of the road.
Several years ago, Virginia replaced all of its Intoxilyzer 5000 machines with EC/IR II machines. The EC/IR II machine uses both an electro-chemical and infrared mechanism. The infrared mechanism does not measure ethanol (alcohol), it simply verifies that the breath sample contains ethanol. Once this verification occurs, a fuel cell in the machine uses an electro-chemical mechanism to measure the amount of ethanol in the breath sample.
Potential Problems with the EC/IR II Machine
There are many things that can interfere with the results from a breath test machine, including but not limited to: (1) radio frequency interference; (2) residual mouth alcohol; (3) higher than normal mouth temperatures; (4) problems with the slope detector on the machine, and (5) fuel cell drift.
In addition, machines malfunction and must be repaired from time to time. When this occurs, the machine in question will need to be tested before results from that machine can be accepted as valid. If not, the results may be inadmissible.
It is critical in any DWI/DUI case that a subpoena is issued to the Department of Forensic Science for certain breath machine records and logs. The records from the breath machine should be obtained from the state so that they can be reviewed for potential issues.
The main problem with the EC/IR II is that, like all breath testing machines, it has to make certain assumptions about people in general. The problem with any assumption is that all people are not alike. The primary example of why making any assumption in breath testing is problematic is best illustrated by partition ratios. The EC/IR II machine makes a major assumption regarding the ratio between the concentration of alcohol present in a person's blood and the alcohol present in the person's lung air. This ratio is called a partition ratio. The machine assumes that each person has a partition ratio of 1:2,100. In other words, the machine assumes that there is one molecule of alcohol in a person's breath for every 2,100 molecules of alcohol in the blood. This is critical because a breath test's fundamental purpose is to measure blood alcohol content - not breath alcohol content. The machine simply uses the breath as a means by which to determine the amount of alcohol in one's blood. The problem with the assumed partition ration of 1:2,100 is that not every person has that exact partition ratio. The idea that every person has the same partition ratio has been rejected by many scientists. Rather, the partition ratio varies from person to person by 60% or more from the 1:2,100 ratio.
This is of critical importance because if a person has a partition ratio of 1:1,100, the test results would overstate that person's BAC by over 50%. For example, if a person were truly a .07 BAC, the machine would read above a .14 BAC.
Not only has Virginia has completely ignored this problem, but the Virginia Legislature has built the fallacy into the law (and effectively taken the issue away as a defense) by defining DUI as "0.08 grams or more per 210 liters of breath as indicated by a chemical test administered as provided in this article." In fact, the Virginia Court of Appeals confirmed in a ruling binding on Virginia courts that DWI defense lawyers are foreclosed from pursuing this argument in DWI cases given the above language in the statute.
Issues relating to the breath machine are highly technical and specialized. A series of vary bad decisions from the Virginia Court of Appeals has made it extremely difficult for DUI defense lawyers to challenge or exclude the official breath certificate of analysis. Therefore, it is more important then ever to focus on challenging the stop and arrest in DUI cases.